1. Field of the Invention
The invention relates to a heat conditioning chamber for controlled cooling following a high-temperature treatment, of plane thin glass sheets, transported in horizontal position by a continuously driven roller conveyor. The invention also relates to chambers which comprise at least two separate independently adjustable cooling zones.
2. Description of the Related Art
When deformations and/or tensions in glass sheets should not occur following a high-temperature treatment, it is necessary to initiate a controlled, slow and regular cooling. This cooling or annealing is performed by convection in a heat conditioning chamber of the tunnel furnace type or not, in which an air current is blown and stirred, the air being blown by crosswise nozzles and sucked into the intake of the chamber in which it circulates in the direction opposite to the direction of transport of the glass sheets (DE--A-1 069 549 and DE-A-1 960 367).
It has been proven that the chambers known in the art do not give satisfactory results in the case of very thin glass sheets, of less than 3 mm of thickness, for example, at least if reference is made to the greatest requirements concerning the surface evenness and the absence of stresses. Such requirements are imposed, for example, for glass sheets intended to be joined by lamination and undergoing, before their forming, a high-temperature treatment. Such a treatment is necessary, for example, to apply current supply electrodes and/or to proceed to baking an enamel framing. Glass sheets thus prepared particularly enter into making heated windshields.
The usual processes do not lead, except in proceeding in an exceptional manner, to an optical quality similar to the optical quality currently obtained for traditional nonheated windshields, mainly because of the state of the glass sheets before their forming. Actually, not to exert a negative influence on the quality of the laminated glazing, each glass sheet should be not only absolutely plane and without deformations but also perfectly free of inner stresses able to generate troublesome deformations during the forming.